Electric discharge tube



Dec. 15, 1936. o. H. BIGGS ELECTRIC DISCHARGE TUBE Filed Nov. 17, 1934 INVENTOR BY d ff7 ATTORNEY Patented Dec. 15, 1936' UNITED. STATES PATENT. OFFICE 7 ELECTRIC DISCHARGE TUBE Orrick Howard Biggs, Beverly, Masa, assignor to Hygrade Sylvania Corporation, Salem, Masa, a corporation of Massachusetts Application November 17, 1934, Serial No."i53,424

6 Claims. (01. 250-275) i many cases-interferes withthe starting orlproper functioning of the device. This phenomenon. is particularly pronounce'din those devices where the enclosing envelope is of a tubular or elongated shape, for example cathode-ray-tubes, gaseous discharge lamps and the like. Various devices have been proposed heretofore for dissipating this unwanted wall charge. For example it has been proposed to seal into the tube wall one or more metal members to conduct away the charges. Another proposal has been to surround the tube with a conducting shield or cage, while a still further proposal has been to coat the inner surface of the tube with a conductive material such as graphite or metal. Entirely apart from the cost of incorporating these special conductive devices is the fact that the opacity of the conducting members or coatings renders them objectionable when applied to lamps, cathode-ray-tubes or the like where light transmission efficiency is the desideratum.

Accordingly one of the principal objects of this invention is to provide a lamp, tubeor similar device with a substantially transparent enclosing envelope which is relatively free from wall charge effects.

A feature of the invention relates to a lamp or tube having one or more electrodes enclosed within .a transparent envelope which is treated to render it inherently conducting without substantially afiecting its'transparency.

Another feature of the invention relates to a discharge lamp or tube with a substantially transparent vitreous envelope having incorporated in the body thereof a conductive. material or materials. v

Another feature relates to a discharge tube or lamp having a substantially transparent vitreous envelope having incorporated therein a conductive metallic salt.

Other features and advantages not specifically enumerated will be apparent after a consideration of the following detailed description and the'apand a gaseous discharge lamp, it will be understood that this is done merely for purposes of illustration and not by way of limitation.

In the drawing Fig. 1 illustrates schematically in sectional view a typical form of cathode-raytube embodying features of the invention.

Fig. 2 illustrates diagrammatically the invention as embodied in a gaseous discharge lamp.

Referring more particularly to Fig. 1 there is --showna"'cat-hode.-ray -tube having a i vitreous V envelope comprising a cylindrical neck portion 1;

a conical body portion 2 and a flattened end wall 3. The neck portion lhas sealed thereto a reentrant stem 4 terminating in a press 5 through which certain of the lead-in wires pass. Suitably mounted within the tube is a heater 8; an electron emitting cathode I; a control electrode 8; a focusing electrode 9; an anode Ill and deflecting plates H. For a more detailed description of a tube of this character, reference may be had to cope'nding application Serial No. 724,878, filed May 10, 1934.

In accordance with the usual practice the interior surface of the end wall 3 is provided with a coating which fluoresces under the impact of the cathode rays. The electrons emitted from the cathode I pass through the opening in the control electrode 8 and thence through the openings in the focusing electrode 9 and the anode ill. By means of suitably variable potentials applied to the deflecting plates H the cathode-ray-beam is oscillated to trace a desired pattern on the screen i2. -Unless particular precautions are taken the stray electrons which strike the inner surface of the vitreous tube produce an electrostatic charge on this surface which chargetends to reduce the velocity of the electrons in the main cathode beam, and tending also to reduce the brightness of the spot on the screen H. The existence of this electrostatic charge also tends to destroy the focus of the cathode beam result. ing in a blurred spot on the screen. In order to prevent the formation of this electrostatic charge the glass or vitreous material constituting the enclosing envelope has incorporated therein a material or materials which impart the desired conductivity to the tube wall. As examples of such materials may be mentioned metallic conductive salts such as stannous chloride, ferric chloride or the like. These conductive materials or salts may be incorporated in the vitreous envelope many well-known manner, for example the stannous chloride may be fused into the body of the glass at approximately about 500 C. This material imparts a slight iridescence to the glass but does not materlallyeifect its light trans mission power.

It will be understood of course that it is necessary, in connection with the tube of Fig. 1, to impart this conductivity to only that portion of the tube where the wall charge eilects tend to exist or be deleterious. For example the cylindrical neck portion i and the stem 4 may be of glass such as is ordinarily employed in lamps, tubes or the like, whereas the conical portion 2 and the wall portion 3 may have incorporated therein the conductive materials mentioned. Consequently when the tube of Fig. 1 is in actual use any wall charge that tends to accumulate is end orseal-in portions II and I5. Portions I3 and I! are fused or otherwise hermetically joined together at the points l6, l1. Sealed into the portion H is a suitable electrode l8 and asimilar electrode I9 is sealedinto the portion 15. To facilitate the sealing, suitable beads 20 and 2| oi. specially chosen glass may be employed if desired. The sealed tube is previously evacuated andthen filled with an ionizable medium such as an inert gas, mercury vapor or any desired mixture of these. Preferably, although not necessarily, the electrodes provided. with electron emissive coatings such as an alkaline earth oxide or a mixture of alkaline earth oxides,as for example are used in the radio tube art. electrodes l8 and I9 are connected in circuit with a suitable source of potential, the ionized discharge through the tube causes a' bombardment ofv one or the other of the electrodes. The gas pressure and voltage may. be so chosen that the bombardment is suiiicient to raise one of the electrodes to a temperature at which it becomes thermionically emissive. It will be understood of course that the invention is not limited to the bombardment method of heating one or both of the electrodes, and that any well known method of heating the electrodes to render them electronically emissive may be employed. It has been found that when the tubular portion 13 of the enclosing envelope has incorporated therein a specially chosen material or materials, the envelope wall becomes sufliciently conductive to prevent the accumulation of an electrostatic charge When the aoaasuo which would otherwise-interfere with the proper starting or operatlonpf the lamp; of these materials which impart the desired conductivity to the envelope wall without substantially afiecting' the light transmission character! istics oi the said wall maybe mentioned stannous chloride, ferric chloride or a mixture thereof.

Various changes and modifications may be made herein without departing from the spirit and scope of the invention. For example while it is preferred to incorporate the conductivityimparting. materials in the body of the vitreous envelope, these materials may be glazed on to the envelope in any well known manner. Fure thermore, while certain spe tfic .materials have been mentioned herein, it will be understood that other similar materials may be incorporated so long as these materials do not materially interfere with the light transmission characteristics of the envelope nor deleteriously affect the life or operating characteristics of the lamp or tube.

As examples The term gaseous discharge as employed herein 'mally conductive vitreous material.

3. A space discharge device comprising an electron emitting cathode, an anode for said cathode, a transparent envelope enclosing said electrodes. said envelope having incorporated therein a quantity of a metallic chloride to impart conductivity to said, envelope without substantially affecting the transparency of said envelope.

4. 'Ihe combination according to claim 3, in which the chloride is stannous chloride.

5. The combination according to claim 3, in which the chloride is ferric chloride.

6. A gaseous discharge lamp comprising a pair of spacedelectrodes between which a visible discharge is to be produced, and a vitreous tubular envelope enclosing said electrodes having a selected portion of the envelope wall of normally conductive transparent vitreous material.

. ORRICK H. BIGGS. 

